I think you are making a hidden assumption. Here is a good question to tease it out: why does it make sense to ask why a coin flip came up heads but not make sense to ask why we observe one QM outcome?

With the coin flip, it’s understood that the probability distribution is not reality. It’s just a way of approximating reality without having to model all the things that would explain our observations.

With QM we have equations that predict probability distributions, and there is debate about whether reality is literally a distribution of possible states, or if it’s more like the coin flip random variable.